1. Field of the Invention
The present invention relates to a root canal post used for treatment of a broken tooth, and more particularly to a root canal post for such use, which is provided on a root tooth to construct a therapeutic foundation with the use of a pasty filler, such as composite resins. In this specification the term "root canal post" includes not only screw posts and molded posts but also auxiliary screw pins for supporting them; hereinafter the term "screw post" is used to represent all other posts.
2. Description of the Prior Art
In order to construct a therapeutic foundation for treatment of a broken tooth, it is known in the art to use a cast metal for it but recently the intracoronal therapy employing composite resins has drawn dentists' attention because of the advantage that the composite resins simultaneously form both the foundation and a post. However the construction of composite resins is fragile as compared with the conventional cast metal; therefore, to compensate for the reduced strength, a screw post is used to reinforce the foundation of composite resins.
In order to explain the background more clearly, referring to FIG. 5, the conventional practice will be described in detail:
The reference numeral 4 denotes a tooth root whose canal has been treated. After the surfacial softening dentitum is removed, a hole 3a is bored by means of a dental drill of a size corresponding to that of a screw post 1 while the retainer is being removed from the root canal. The hole 3a is filled with a dental cement 5, and simultaneously the screw post 1 is forced into the hole 3a. The screw post 1 has threads 1a whereby it is securely anchored in the hole 3a. Optionally the screw post 1 is reinforced by a screw pin 2 inserted into the tooth root. Then a composite resin 9 is applied to cover the screw post 1, and allowed to harden. The contour of the bulge of the resin is shaped by means of a diamond point so as to be adapted for the tooth root 4. Finally an artificial crown 8 is fitted.
However dental cavities are likely to occur again in the treated tooth. In such cases it will be required to withdraw the screw post 1, which, however, is very difficult or almost impossible to do because of the firm anchorage of it in the bed of cement 5. As a result, the tooth must be wholly extracted. In general the intracoronal treatments are expensive, but if the treatment of a secondary infection (secondary cavity) is required any price spent on the previous treatment will be wasted.